Mike Petrosino wanted to say one last goodbye to his best friend, Rusty.

The 21-year-old man, who is dying of cancer, was greeted by his childhood dog at Massachusetts General Hospital on Friday. The moment was captured by his brother, John, who later shared it with a friend, and it has since gone viral on Reddit.

“My friend Mike was diagnosed with cancer in the 8th grade. He was given a 3 percent chance to survive the first year. Two days ago we found out that after 8 years, the amputation of his leg, and four rounds of cancer that there's now nothing they can do,” Redditor 7thEvan wrote. “He's the bravest guy I've ever met, and all he did the entire day was make sure everyone else was okay.”

Petrosino was diagnosed with metastatic Ewings Sarcoma, a rare bone cancer, just two months shy of his 14th birthday. After a year of aggressive chemotherapy and radiation treatments, he was in remission. But, in April of his senior year of high school, Petrosino’s cancer returned. After several years of treatment and surgeries, including one that amputated his right leg and pelvic bone, doctors expect Petrosino to succumb to his illness within a few days, TheBlaze reports.

“That was by far one of the most touching moments of my life,” Petrosino’s brother, John, told TheBlaze about the moment he captured on Friday.

“Rusty was very emotional when Mike said his final goodbye,” John said about the 10-year-old dog. “Every time I come home these past two days, he sits near Mike’s favorite couch and whines, which is rare from him.”

In June, Petrosino’s mother, Paula, created a GoFundMe page to pay for the travel expenses related to her son’s treatment. “After everything he has gone through, he does not complain or say, 'Why me?' He is the strongest person I know and he is my hero,” she wrote.

John Petrosino said watching his brother with their childhood dog made him smile. His Facebook page is flooded with well-wishes and memories.

“My mom reminded me of a story from when i was about 6 and mike was about 5, we were camping at kingston lake and we were holding hands and running around saying we’ll always be brothers,” he posted on Dec. 17.  “Mike's always been my best friend. Just thinking about him and i tear up now. Im [sic] so proud of how hard he fought. I dont consider this a loss, mike just needs a rest of the pain hes recived these past 8 years. I know he’ll be watching me and our niece Olivia.”